Automated identification of articles is a recent phenomenon which finds its advent in the invention of the integrated circuit and the availability of computing power at reasonable costs. In the late 1960's, for instance, a number of companies began to develop practical automated supermarket checkout systems, and a pilot system was installed in a Kroger store in Cincinnati, Ohio in 1967. One of the first scanners capable of reading the Universal Product Code bar code was installed at a supermarket in Troy, Ohio in 1974. More than 90% of all grocery items carried a UPC code by 1980. Since 1980, a torrent of information has been published on bar codes, and by December 1985, more than 12,000 grocery stores were equipped with scanner checkout systems. See, e.g., C. Harmon and R. Adams, Reading Between the Lines--An Introduction to Bar Code Technology (Helmers Publishing, Inc. 1989).
Bar codes have also been used for identification and characterization of responses to mass advertising efforts. U.S. Pat. No. 4,752,675 issued Jun. 21, 1988 to Zetmeir, for instance, discloses devices and methods for reading bar codes placed on advertising materials sent to particular addressees. The information interpreted from the bar codes is compared with master file lists for analysis of the effectiveness of the advertising.
Bar codes are typically read using lasers which scan from left to right, right to left, or in both directions (or other directions) across a field of alternating dark bars and reflective spaces of varying widths. Multiple scans are typically employed to minimize data errors. Because of the multiplicity of bars and spaces required for each alphanumeric character, bar codes require a relatively large space to convey a small amount of data. For instance, each character in the bar code system known as Code 39 requires five bars and four spaces. A high density Code 39 field corresponds to only 9.4 characters per inch.
Universal Product Codes are another common bar code. They are used primarily in the retail grocery trade and contain a relatively large number of bars and spaces which allow for error checking, parity checking and reduction of errors caused by manual scanning of articles in grocery stores. They accordingly require even larger space for conveyance of character information, in relative terms.
The Codabar code, which has been developed by Pitney Bowes and is used in retail price labeling systems and by Federal Express, is a self-checking code with each character represented by a stand-alone group of four bars and three interleaving spaces. Federal Express uses an eleven digit Codabar symbol on each airbill to process more than 450,000 packages per night. Other codes use varying bar and space techniques to represent characters. Because of error checking requirements and for other reasons, however, the space required to place a bar code on an article is relatively large.
In addition to the large surface area required for the series of bars and spaces that form a typical bar code symbol, the code must be placed on a background that has a high reflectance level. The high level of contrast, or reflectivity ratio, between the dark bars and the reflective spaces, allows the optical sensor in the reader to discern clearly and dependably the transitions between the bars and spaces in the symbol. Ideally, the printed bar should be observed as perfectly black and the spaces should be perfectly reflective. Because those ideal conditions are seldom possible, the industry typically requires that labeling media reflect at least 70% of incident light energy. Surface reflectivity and thus quality of the media on which the bar code is placed directly affects the successful use of the bar code on that media. Additionally, the media cannot be overly transparent or translucent, since those characteristics can attenuate reflected light. Accordingly, only limited types of highly reflective media may be used for placement of bar codes.
Space requirements for bar codes further include a "quiet zone" which must surround the field of bars and spaces. In many codes, this quiet zone constitutes a border of 1/4 around the code symbol, thus requiring even more space for the bar code. These space and reflectivity limitations often require bar codes symbols to be conspicuous and aesthetically obtrusive.
Bar coding also requires very precise print methods. Assuming that the printing operation is capable of printing the required density to achieve the 70% reflectance ratio, careful attention must be paid to additional major factors that influence the bar code effectiveness. Those include ink spread/shrinkage; ink voids/specks; ink smearing; non-uniformity of ink; bar/space width tolerances; edge roughness and similar factors which must be closely controlled to ensure that the symbol will be easily scannable. In other words, the printer must pay careful attention to using paper or other media that displays the correct absorption properties properly inking the ribbon; carefully controlling hammer pressure; keeping the printhead and paper clean; properly wetting the paper and curing the ink; and maintaining proper adjustment of the printhead control mechanism. These printing details create additional problems and expenses, particularly for placement of bar code symbols on smaller items such as coupons and mail pieces.